This invention relates generally to film cooled combustor liners for use in gas turbine engines, and more particularly, to such combustor liners having regions with closely spaced cooling holes.
Combustors used in aircraft engines typically include inner and outer combustor liners to protect the combustor and surrounding engine components from the intense heat generated by the combustion process. A variety of approaches have been proposed to cool combustor liners so as to allow the liners to withstand greater combustion temperatures. One such approach is multi-hole film cooling wherein a thin layer of cooling air is provided along the combustion side of the liners by an array of very small cooling holes formed through the liners. Multi-hole film cooling reduces the overall thermal load on the liners because the mass flow through the cooling holes dilutes the hot combustion gas next to the liner surfaces, and the flow through the holes provides convective cooling of the liner walls.
However, multi-hole film cooling is more difficult to design compared to pure nugget cooling due to the many restrictions associated with it, such as, the limitations on the spacing between holes, the number of holes in each row of multi-holes, the limitations on hole sizes, and difficulty of doing preferential cooling, for example. Specifically, to provide adequate cooling, the holes should be spaced an adequate distance from each other to facilitate applying the thermal-barrier coating (TBC) to the combustor, and should also be spaced sufficiently close to each other to establish good film and convective cooling.
For example, to achieve adequate combustor cooling, at least one known combustor includes cooling holes that are spaced equidistantly in an axial direction and no attempt is made to control the circumferential spacing. However, since many liner contours have changing slopes, the circumferential spacing may vary uncontrollably, resulting in liners having areas that are overcooled and other areas that are undercooled. Moreover, circumferential preferential multihole cooling is difficult to fabricate because it requires variable circumferential spacing, which may cause interference among multihole rows. Additionally, varying hole sizes is a possibility for circumferential preferential cooling, but it is relatively difficult to maintain the axial and circumferential distances between holes within the design limitations and also introduces additional cost.
Accordingly, there is a need for a combustor liner in which cooling film effectiveness is increased in the areas of the liner that are subject to unusually high temperatures and resulting material distress.